This invention deals with new and novel polymethyl (disilyl)silazanes. a method for their preparation, their use to prepare ceramic materials, and the ceramic materials prepared thereby. Said invention resides in the use of certain cyclic silazanes, or mixtures of them, as coreactants with halogen-containing disilanes to give the unique polymethyl(disilyl)silazane polymers.
Since about 1975, there has been a renewed effort in the synthesis of preceramic polymers owing to the fact that such polymers have handling properties which allow the formation of shapes and forms prior to ceramification. Thus, several different methods have been developed and disclosed for the preparation of polymethyl(disilyl) silazane polymers that can be converted to silicon nitride-containing ceramics and other related materials.
The first reported method is that disclosed by Gaul, in U.S. Pat. No. 4,340,619, issued July 20, 1982 in which he obtained ceramics materials by pyrolysis of preceramic polymers, which polymers were prepared by reacting chlorine-containing disilanes and disilazanes. These polymers were pyrolyzable to silicon-carbonitride Si-C-N ceramics and prior to pyrolysis, the polymers were capable of being handled i.e. shaped or molded and thus one could form such things as fibers from such polymers.
Other polymer precursors for forming silicon nitride ceramics have been described. Verbeek in U.S. Pat. No. 3,853,567 issued on Dec. 10, 1974 discloses the reaction of methyltrichlorosilane reacted with methylamine to form methyltris(methylamino)silane. This product could be heated to form a polymer at 520.degree. C. The polymers could be cured by moist air oxidation at 110.degree. C. and then pyrolyzed to afford a low yielding Si-C-N-O ceramic. Similar materials and techniques were disclosed by Verbeek. et. al. in U.S. Pat. No. 3,892,583, issued July 1, 1975.
Gaul, in U.S. Pat. No. 4,321,970, issued Jan. 26, 1982, discloses the preparation of polysilazane polymers that were synthesized by reacting various alkyltrichlorosilanes with hexamethyldisilazane ({(CH .sub.3).sub.3 Si}.sub.2 NH). In this synthesis, (CH.sub.3).sub.3 SiCl was eliminated as a by-product. These materials could be pyrolyzed at high temperatures to form Si-C-N containing ceramics.
Cannady in U.S. Pat. No. 4,543,344, issued July 3, 1985, described a modification to Gaul's process to include the preparation of a polyhydridomethylsilazane polymer from trichlorosilane and hexamethyldisilazane, the same inventor in U.S. Pat. No. 4,540,803, issued Sept. 10, 1985 showed that these polymers were capable of being pyrolyzed to Si-C-N type ceramics.
Additional polymers have been developed and disclosed by Gaul in U.S. Pat. No. 4,395,460, issued July 26, 1983; U.S. Pat. No. 4,404,153, issued Sept. 13, 1983; Haluska in U.S. Pat. No. 4,482,689, issued Nov. 13, 1984; Seyferth et al., in U.S. Pat. No. 4,397,828, issued Aug. 9, 1983; Cannady in U.S. Pat. No. 4,535,007 issued Aug. 13, 1985; Bujalski, U.S. patent application Ser. No. 653,003, filed Sept. 21, 1984; Baney et al., U.S. patent application Ser. Nos. 652,938, filed Sept. 21, 1984 and 653,939, filed Sept. 21, 1984.
What has been discovered are new and novel preceramic polymers, methods for their preparation, their use to prepare ceramic materials and the ceramic materials prepared using such preceramic polymers.